<PRE><B>Question 148507</B>
1. y=5x+3  5x-y=7


Substitute 5x+3 for y in the second equation

5x-(5x+3)=7


Simplify
5x-5x-3=7


-3=7
**no solution**
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2. 3x-2y=5 2y=3x+7 


Plug in 3x+7 for 2y

3x-(3x+7)=5


Simplify
3x-3x-7=5


-7=5
**no solution**
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3. x-3y=13  3x=9y+39   

Multiply the first equation by 3.
3(x-3y=13)  3x=9y+39 


3x-9y=39  3x=9y+39 


Add 9y to both sides in the first equation


3x=9y+39  3x=9y+39 
**infinitely many solutions**
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4.x+4/5y=4  x-1/2y=-9


Subtract the second equation from the first
1.3y=13

y=10


Plug 10 in for y in the first equation
x+4/5(10)=4
or


x+8=4

x=-4


So **y=10 and x=-4.**</PRE>